Television system and method



Jan. 7, 1936- D. J. BAKER TELEVISION SYSTEM AND METHOD Filed April 11,1932 Sheets-Sheet 1 FIG. 30

FIG. 3a

FIG 40 DONALD J BAKER Jan. 7, 1936. D. J. BAKER TELEVISION SYSTEM ANDMETHOD FIG. 5b

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FIG-4d DONALD J. BAKER Jan. 7, 1936- D. J. BAKER TELEVISION SYSTEM ANDMETHOD Filed April 11, 1932 4 Sheets-Sheet 3 e/vvbom DONALD J. BAKERJan. 7, 1936. J, A 2,026,725

TELEVISION SYSTEM AND METHOD Filed April 11, 1952 4 Sheets-Sheet 4Ill/IIIIIIIIII/lI/IIIIIIIIII/ '1 llll lll FIG. 10

Patented Jan. 7, l

J UNITEDTSTATES PATENT. OFFICE v 'rELnvIsroN' szlfiaun m'rnop DonaldJerome Baker, Hartford, Application Aprllll, 1932, Serial No. 654,622 19Claims. (01. 178-4) ning method of the prior art and does not employmoving mechanical parts.

A further object of my'invention is to devise a television system whichis self-synchronizing, that is, when the system isproperly adjusted.synchronism is inherently maintained between the transmitter and thereceiver without attention from the operator, and without employingspecial synchronizing apparatus.

Still another object of my invention is to devise a television systemwhich operates upon a relatively narrow band of transmission frequenciesas compared with the band required by systems now 20 in use. I

Another object is to devise a television system which is positive inoperation, simple of construction, and, therefore relativelyinexpensive. In prior television systems, the method of transmissioninvolves scanning the image to be transmitted one elementary area at atime, transmitting successive current impulses corresponding in lightintensity to the difierent elementary areas forming the image, and atthe receiving corresponding light variations which are distributed upona receiving screen in the same order in which the original image wasscanned. In such systems where only a single point of the image isscanned at any instant, it is necessary to cover in succession all theelementary areas forming the image and at such a rate that the imagemust be completely scanned 16 or more times per second. In thetelevision system which I have devised the entire image is scannedinstantaneously by a horizontal scanning element and at the same timethe entire image is. scanned instantaneously by a vertical scanningelement.

45 Two transmission channels are provided, one for station these currentimpulses are translated into my copending application Serial No.573,961, filed November 9, 1931.

My invention is illustrated in the accompanying' drawings in which:

Figure 1 is a vertical sectional view illustrating 6 the constructionoione form of receiving tube employed at the receiving station;

Figure 2 is a front elevational view of the tube' shown in Figure 1;

Figure 3a is a front view of the cathode element 10 employed in Figure1;

Figure 3b is a sectional view along line b-b in Figure 3a;

Figure 4a is a side elevational view oi! one of the grid elementsemployed in Figure 1;

Figure 4b is an end view of Figure 4a;

Figure 4c is an enlarged fragmentary view 11- lustrating the details ofconstruction of Figure 4a;

Figure 4d is an enlarged broken view of a sec- 0nd form of gridconstruction;

Figure 4c is a sectional view of Figure 4d taken along line e-e.

Figure 5 is an elevational view partly in section illustrating aprojector receiving tube assembly on a reduced scale;

Figure 5a illustrates another form of projector for intensifying thereproduced image; I

Figure 5b is a sectional view illustrating the details of constructionof. the fluorescent plate employed in Figure 5a;

Figure 6 is a vertical sectional view illustrating 'the construction ofone form of light sensitive cell employed in the transmitting station;

Figure '7 is a front elevational view 01 Figure 6;

Figure 8 is a vertical sectional view of a second form of transmittingcell; V

Figure 9 is a plan view in section showing a third arrangement oftransmitting cell;

Figure 10 is a vertical sectional view illustrating 40 the constructionof a fourth form of transmitting cell;

Figure 11 is a schematic circuit diagram of my complete televisionsystem;

Figures 11a and 11b illustrate modified forms of circuit closersemployed in Figure 11;

Figure 12 is a simplified circuit diagram for explaining the operationof the system.

Referring to Figure 1, the tube employed at the receiving station fortranslating the receiving current variations into corresponding lightvariations comprises a glass envelope I provided with a base 2 which inturn is provided with a number of connecting prongs 2a.. The envelope Iis provided with a clear'circular window la ontowhich the receivedpicture is to be impressed. On the inside of this'window section isformed a fluorescent target 3 comprising a thin transparent film of goldor other highly conductive metal deposited on the glass window and ontop of this conductor film is deposited a layer of material 3b whichfluoresces under bombardment of electrons, such for example, asWillemlte or other similar material. An electron emitting cathodeelement 4 having an active surface substantially as large as thefluorescent screen 3 is mounted parallel to the screen within the tubeas shown. Interposed between the screens 3 and the oathode 4' are twocontrol grid elements 5 and 6 arranged parallel to the screen and to thecathode, with their grid wires running at right angles to each other. Inthe arrangement shown in Figures l and 2 the wires in grid 6 arevertical, while the wires in grid 5 run horizontally. The details of theconstruction by which elements 4, 5 and 6 are mounted within the tubehave been omitted for the sake of clearness of showing, and the mannerin which these elements may be supported will be obvious to one skilledin the art.

The annular portion of bulb i surrounding the window la is covered withan opaque coating 2b, such as a metallic foil coating. A second opaquecoating 20 is applied over the back portion of the tube, leaving a cleartransparent annular portion 2d extending entirely around the tubebetween the two opaque coatings. It will be understood that elements, 3,4, 5 and 6 are shown in side elevation in Figure 1, while the tube andits base 2 are shown in sectional view. Each of elements 3, 5 and 6 areprovided with a connection to corresponding prongs 2a, and the heatingcoil in the cathode 4 is connected to two of the prongs 2a. Theseconnections have been omitted from Figures 1 and 2 for the sake ofclearness of showing.

The details of construction of the cathode element 4 are illustrated in.Figures 3a. and 3b. This element is formed of an electron emittingmetallic plate 4a which faces the grid elements 5 and 6. This plate istreated in a well known manner or coated with a suitable substance toincrease its capacity for electron emission. Plate 4a is mounted upon aninsulating, heat resisting backing plate 4b, which is provided with achannel to receive a heating coil 40, which is retained in position inthe channel by an insulating, heat resisting filler material 4d. Theelectron emitting plate la is secured to the base plate 41) by suitablerivets or screws passing through the entire assembly and engagingclamping plates 4e arranged around the outer edge of each side of thecathode element. The backing plate 4b may be formed of any suitableinsulating, heat resisting material such as Isolantite or the like, and

the filler material 4d may be any suitable ceramic material which ishighly heat resistant and insulating. It is obvious that instead ofemploying a channeled backing plate 4b, the heating coil 4c may beincased in a solid plate at the time of molding the plate. The heatingcoil would then be baked into the plate as a complete unit. It will beunderstood that the heating coil 40 is so arranged that the entiresurface of plate 411 enclosed within the clamping strips 4e emitselectrons from each elementary surface at the same rate.

The details of construction of one form of grid elements 5 and 6 areillustrated in Figures 4a and 4b. The two grids .are the same inconstruction, but they are so mounted that the wires in the two gridsare arranged at right angles to each I other. The grid element is formedof two side members 5a and 5b made of suitable insulating, heatresisting material. Two rods 50 and 5d are screw-threaded into the endsof side-piece Ia, and side-piece 5b is provided with holes in each 6 endto slldably receive the free ends of the rods 50 and 5d. Expansionsprings 5e and 5! are arranged on rods 5c and 5d respectively and tendto push side-pieces 5a. and 5b apart. Each of side members 5a. and 5b isprovided with a numl0 ber of holes arranged in staggered relation in tworows as shown. The object of staggering the holes is to permit the useof a relatively large hole for a small spacing between adjacent bars ofthe grid. The vertical .distance of separation 1 of adjacent holes isequal to the desired separation between the grid wires. A single wire 5gis threaded through the holes to form a continuous grid beginning at oneside of the frame and ending at the other and passing back and forth be-20 tween the side members 5a and 5b. By threading the grid wire '51through the holes in the manner shownv in greater detail in Figure 4c,the wires forming the grid lie in the same plane on one side of the gridframe. In order that the 25 two grids may lie as close together aspossible, the two grid elements 5 and 6 are arranged with their gridsfacing each other as shown in Figure 1, but not in contact with eachother. In winding the grid elements. the side-pieces are 30 pressedtowards each other to compress springs 56 and 5f; the grid wire is thenthreaded onto the frame in the manner shown in Figure 4c, and then theside-pieces are released. The springs 5e and 5!, by pressing the sidebars apart, keep the 35 grid wire under constant tension and prevent thegrid bars from sagging due to unequal expansion between the wire and theframe with changes in temperature. The wire 59 forming the grid shouldpreferably be of a very small size, and the 40 spacing of the adjacentbars of the grid may be arranged to suit the detail required in thepicture; a close spacing giving greater detail than a wide spacing. Thespacing between adjacent grid bars will, of course, correspond to thedimen- 45 sion of an elementary area of the picture being transmitted orreceived, and this will depend upon the degree of detail desired in thetransmission. 5

A second form of construction for the grid ele- 50 ment is illustratedin Figures 4d and 42. In this construction, the insulating side members5a and 5b, which may be made from Isolantite, are not provided withholes or apertures for receiving the grid wire, but a series of narrowslots 5h are cut 55 in one side of the side members, thus forming aseries of equally spaced ribs 5i along one face of each side member. Theslots 5h are cut at an angle to the face of the side member so that theslots cut through one corner of the side member and emerge on theadjacent face. A groove or slot 510 is formed in the adjacent sidethroughout the length of each side member for the purpose of forming anotch or heel on each rib 52' for receiving and retaining the loops ofwire 5g forming the grid. As will be seen from the drawings, the ribs ofside member 5b are staggered with relation to the ribs of the sidemember 5a, and the width of the slots Sn and the thickness of theribs51' are suitably chosen to produce uniform spacing between adjacent barsof the grid wire 5g. It will be understood that the grid is formed bylooping the wire 5g over the slotted ends of the ribs 51' and passingalternately from a rib on one side member to the next rib on the otherside member. It will be seen that this construction presents a moreeasily assembled grid than that illustrated in Figures 4a and 4b. Theside members 5a and 5b are held apart by double-ended screws 5m and 5n,the opposite ends of which are providedwith right and left screwthreaded engagements with spacing bars 5p5q and 5r--5s respectively. Byadjustment of the double ended screws 5m and 5n, the side members 50 and5b may be forced apart to apply the proper tension to the grid wire 557after the same is wound upon the grid frame.

It is apparent that Figures 3a. 3b, and 4a to 42 are not drawn to scale,but the dimensions have been exaggerated in some cases for the sake ofclearness of showing.

Figure 5 illustrates the construction of a projector for the receivingtube shown in Figure 1. This projector comprises a parabolic or ellipticreflector I having a highly polished interior surface and provided witha cover Ia over its front end. The cover la is provided with a centralopening over which the tube I is placed with an annular layer of felt orother resilient material '10 interposed. The tube I is supported in asocket 8 which in turn is supported by a bracket 'Ib secured to thereflector I. The lamp socket 8 is provided with usual connector contactscooperating with the tube prongs, and a wire cable 8a is provided tolead the connections out of the reflector 1. An incandescent lamp 9provided with a base 9a is also mounted upon bracket 1b, and the supplycircuit for this lamp is provided through the conductors of cable 8a.The lamp 9 is located approximately at the focal point of the reflectorI. A lens tube Id is mounted on the front of the reflector cover Iaimmediately in front of the opening in which the tube I is mounted. Asshown by the two dotted lines proceeding from the lamp 9, the rays oflight from the lamp are reflected by the polished inner surface of thereflector-and pass through the transparent portion 2d of the tube I andilluminate the fluorescent. screen 3 within the tube. Any picture whichis impressed upon this screen will, therefore, be projected through thelens tube Id onto an enlarged screen outside of the projector. In Figure5 the projector 1, its cover Ia, felt strip 10 and the lens tube Id areshown in ver-. tical sectional view, while the remaining elements areshown in side elevation. It will be understood that the receiving tube Imay be used without the projector shown in Figure 5, by viewing directlythe image formed on the screen 3.

A second form of projector for intensifying the reproduced image isillustrated in Figure 5a. In this arrangement the receiving tube isdiagramratically illustrated at R and comprises an electron emittingcathode 4, two grid elements 5, 6 and a fluorescent plate anode 3. Asource of intense light, symbolized by the lamp L provided with areflector M, is arranged to illuminate the backside of the fluorescentplate 3 with light of uniform and constant intensity. A reflecting.

mirror N is arranged in the path of light reflected rom the fluorescentplate and is so positioned that the light reflected from its reflectingsurface is directed along the axis of a lens tube P. This projectingarrangement may conveniently be enclosed in any suitable housingdiagrammatically illustrated by the dotted square H.

The construction of the cathode element 4 and the grid elements 5 and Bof Figure 5a may be in accordance with any of the constructionsdescribed hereinbefore. Fluorescent plate 3 may, if desired, be formedupon the front wall of the enclosing envelope after the mannerdescribedin connection with Figure 1. Another form of construction ofthis fluorescent plate is illustrated in 5 Figure 5b. The platecomprises a transparent plate 3 of insulating material such as glass orPyrex, on one face of which is deposited a thin transparent film ofgold- 3a, and deposited upon this fllm of gold is .a layer offluorescent material 10 3b such as Willemite. In order to provide a goodelectrical connection to the gold film and the fluorescent surface, theplate 3, before the film is deposited, is first provided with twoshallow slots 30 and 311 on opposite sides in the face of the 15 plateto receive the film. Silver or platinum is then deposited in the slots,as well as upon the two adjacent edges of the plate, to a thicknesssuffi'cient to fill the slots, thereby forming metallic corners 3e and 3for the plate. Both faces of 20 the plate are then ground to a smoothfiat surface, and then the transparent film of gold 3a is deposited uponthe face of the plate 3 and extends over and into the contact with themetallic corner members 3e and 3f. Instead of providing the plate 3 witha metallic border on two edges only, it is obvious that this metallicborder may be provided around the entire periphery of the plate. Thismetallic edge affords a means for obtaining good electrical connectionwith the transparent gold film. It is understood that the dimensions inFigure 5b are greatly exaggerated and .are not to scale.

In the operation of the projector shown in Figure 5a, the transparentfilm of gold on the fluorescent anode 3 is a very good reflector of thelight from the source L, but the fluorescence of the Willemite layersuperimposed upon the gold film decreases the reflecting quality of thegold film in proportion to the amount of fluorescence. 40 Accordingly,when different areas of the plate 3 fiuore-"ce to different degrees inaccordance with a picture being transmitted from a distant transmittingstation and impressed upon the receiving tube R, the amount of lightreflected from the 45 different areas on the plate 3 from source L andonto the reflecting surface N will vary according to the changing lightvalues of the picture being transmitted. The light rays forming an imageof the received picture are reflected from the re- 50 fleeting surfaceN' through the lens tube P and onto any suitable viewing screen.

One form of light sensitive tube or cell employed at the transmittingstation for translating light variations into electric currentvariations is illustrated in Figures 6 and '7. The cell comprises aglass envelope Ill provided with a base I 0a and a reentrant stem havinga ring IIlb formed on its end for supporting the elements of the cell.Thebase Ilia is provided with a number of connecting prongs Illc forbringing out connections to the elements enclosed within the tube. Thefront of the envelope I0 shown to the left is substantially flat and isformed of clear optical glass. Behind this clear portion is 10- cated alight sensitive element formed of a clear glass plate II, one side ofwhich is coated with a transparent conductive film I Ia such as a filmof gold, and on top of this film is a layer of light sensitive materialII b, such as a caesium or potassium surface. A metallic frame II c isprovided around the outer edge of plate I I and serves to afford a meansfor making an electric connection to the light sensitive element, theframe being connected to one of the prongs Mic. The

active area of the light sensitive element is sumciently large toreceive acomplete image of the object or scene to be transmitted. Behindthe light sensitive element is located a vertical screen grid I2 and ahorizontal grid I3. These two grids are constructed in the same manneras the grids shown in connection with Figure 1 and illustrated ingreater detail in Figures 4a, 4b and 40. A plate or anode element I4 islocated behind the grid I3 as shown. All the elements II, I2, I3 and Ilmay be supported from the stem "lb of the tube in a manner which isobvious to one skilled in the art. The actual supporting extensions havenot been shown'for the sake of cleamess of illustration. Each of theseelements is connected to one of the connecting prongs IOc on the base I0a as shown.

Instead of employing the construction shown in Figure 6, the lightsensitive element may be formed by replacing the glass plate I I and theconductive film Ila. with a fine wire grid .or mesh stretched across theframe He and on which the light sensitive material III: will bedeposited and supported. The wires forming the mesh may be so small thatthey will not materially obstruct the light rays forming the image to betransmitted, and at the same time this wire screen serves to provide aneffective electrical connection to the light sensitive surface. Thefluorescent screen 3 employed in the tube shown in Figure l-may beformed in a similar manner.

Another form of light sensitive cell for use at the transmitting stationis illustrated in Figure 8. This form of cell employs a light sensitivecathode I I having the same construction as that shown in Figure 6, andalso a vertical grid element I2 and a horizontal grid element I3 of thesame construction as described above. These grid elements are onlyschematically indicated in Figure 8. This form of cell is not providedwith a plate element I4 as shown in Figure 6. Also, the image of thepicture or object to be transmitted is projected upon the lightsensitive element through the screens I2 and I3, and the electronsemitted from the surface of the cathode I I travel back to the anodescreens in a direction opposite to the impressed light rays.

A third form of light sensitive cell is illustrated in Figure 9, whereI5 indicates a light tight housing for the cell provided with a lenstube I511. The light sensitive cell proper, located within the housingI5, comprises a glass envelope I6 enclosing a light sensitive cathodeplate II, both sides of which are coated with light sensitive material.On one side of cathode plate II is located a grid anode element I2, andon the other side a grid anode element I3, with the grid bars of the twogrid elements arranged at right angles to each other. Mounted within thehousing I5, and immediately in front of the lens tube I5a, is a prism I!for dividing the incoming rays into two paths, one leading to prism I8and the other to prism I9. As shown by the arrows, prisms I I, I8 and II! serve to impress identical images on opposite sides of the lightsensitive cathode II. It is obvious that prisms I8 and I9 may bereplaced by suitable mirrors.

The cathode elements II of Figures 6, 8 and 9 may be constructed inaccordance with Figure 5b by substituting a layer of light sensitivematerial for the layer of fluorescent material.

Since it is not necessary for the light rays forming the image beingtransmitted to pass through the cathode plate II in the tubesillustrated in Figures 8 and 9, these plates, as well as the metalliccoating deposited thereon, may be replaced by suitable metallic platesfor'supporting the light sensitive substance.

In Figure 10 I have illustrated alight sensitive 5 cell arrangementwherein the sensitivity of the cell is increased by the use of infraredrays or any other penetrating ray, suchas X-ray or ultraviolet. In thisarrangement a light sensitive cell indicated at is enclosed within alight tight in housing 2| which is provided with a lens tube 2 Iacovering the optical aperture in front of the face 20a of the cell. Theinternal construction of the light sensitive cell is like that shown inFigure 6, and correspondingelements are indicated by 16 correspondingreference numerals. Casing 2I is. provided with an annular light tightcompartment 2Ib surrounding the front end of the light sensitive celland in which is located one or more light sources 22 which emit infraredrays. The 20 infrared ray source may be a single lamp of annular formarranged in the annular compartment or a series of small bulb shapedlamps may be arranged at different points around the compartment. Thecompartment 2I b is cut off from 25 the rest of the housing by an opaqueannular window 2Ic, which cuts off visible light but allows infraredrays to pass through and impinge upon the light sensitive cathode II.The light filter window 2Ic may be formed of an ordinary glass windowcoated with copper oxide, or it may be formed of a thin sheet ofebonite. The action of the infrared rays upon the light sensitivecathode I I causes the image formed on the cathode by lens tube 2Ia tobe more clearly defined and to produce greater electron emission fromthe oathode surface.

Figure 11 is a schematic circuit diagram illustrating my completetelevision system. A transmitting station is shown at A and thereceiving station at B. The light sensitive cell employed at station Amay be any of the cells described hereinbefore, but the arrangement ofthe tube elements shown corresponds to the tube constructionsillustrated in Figures 6 and I0, and like ele- 46 ments are indicated bycorresponding reference numerals. The plate element I 4 is connected tothe light sensitive cathode I I through battery 23, and this plateelement supplies a biasing-potential tending to draw the electronsemitted from the 50 cathode I I to the plate along straight pathspassing through the grid elements I2. and I3. Vertical grid I2 isconnected to the cathode I I through a biasing battery 24 and aresistance 25. Likewise horizontal grid I3 is connected to cathode IIthrough a battery 26 and a resistance 21. The input terminals ofamplifier 28 are connected across the terminals of resistance 21, andthe output terminals of this amplifier are connected to'transmissionchannel I. Likewise the input terminals of amplifier 29 are connectedacross resistance 25, and the output terminals are connected in asuitable manner to transmission channel 2. These two channels may bewired circuits, in which case the amplifiers 28 and 29 would have directconnection to the line wires, or the channels may be radio channelsemploying carrier waves of different frequencies. In case radio channelsare employed, it is obvious that suitable wave generators and modulatorswill be provided for converting the currents supplied by amplifiers 28and 29 into modulated waves for transmission over the channels. Onechannel may be a radio channel and the other a wire channel.

The object to be transmitted is represented as an arrow at 0, an imageof which is formed on cathode II by the lens tube in front of the lightcell. Arranged immediately in front of the lens tube is a rotatingchopper disc CD, which is driven at a speed to interrupt the light raysentering the lens tube at a rate of 16 times per second or higher.Instead of using chopper disk CD, a chopper switch CS may be inserted inthe oathode lead and operated by a suitable motor Ma to interrupt andclose the cathode circuit '16 or more times per second. When using thechopper disk, the switch CS will be left in a position to complete thecathode circuit or will be .short-circuited by a suitable switch. Theobject of both forms of chopper devices is to render the transmittingtube effective for short intervals in rapid succession or at a rate of16 or more times per second.

At the receiving station B, channel I is connected to the inputterminals of an amplifier and channel 2 is connected to the inputterminals of an amplifier 3|. It will be understood that where thechannels involve the use of radio waves, suitable detecting devices areprovided in front of the amplifiers 30 and 3|. Cathode 4 of the receiving tube is maintained in an electron emitting condition by means ofheating battery 32. Vertical grid 6 is connected to the cathode circuitin series with the output circuit of amplifier 3| and in series withbiasing battery 33. Likewise horizontal grid 5 is connected to thecathode circuit in series with the output circuit of amplifier 30 and abiasing battery 34. Batteries 33 and 34 may not be required for alltubes, depending upon the tube characteristics. The fluorescent anodescreen 3 is connected to the cathode circuit through a battery 35 whichmaintains the screen at a high positive potential with respect to thecathode. In the lead to cathode 4 is arranged an automatic switch orinterrupter indicated at AS and comprising a vibrating contact 4|operated by a magnet 42, and a cooperating fixed contact 43. The magnet42 is energized from one of the transmission channels through suitabledetecting and amplifying devices 44, a suitable phase adjusting device45, and a switch 46. The arrangement is such that the contact 4|operates in response to the group frequency of the waves transmittedfrom station A; in other words, in response to the frequency ofoperation of chopper disk CD or chopper switch CS. If desired, vibratingcontact 4| may be a reed contact having means for adjusting its naturalperiod of vibration to correspond to the group or interruptionfrequency. Also, the circuit of magnet 42 may be electrically tuned tothis frequency.

Instead of using the automatic switch AS, the same result may beobtained by viewing the fluorescent plate 3 through a chopper disk 41driven by a motor Mb. The speed of the disk 41 is automaticallymaintained at the proper value by a small synchronous motor 48 mountedoh the same shaft and energized by the group frequency currents suppliedover one channel and through devices 44 and 45. In using the disk 41,the switch 46 is thrown to the left and the switch AS is set to closethe cathode circuit, or a short-circuiting switch may be provided aroundthe switch AS.

A second form of switch AS is shown in Figure 11a. In this arrangementthe magnet 42 is connected in the plate circuit of a gaseous relay 49 ofthe thyratron type, the input circuit of which is to be connected to theswitch 46. The plate circuit of the relay is completed through a fixedcontact 50 cooperating with the armature 4| in such manner as to openthe circuit when the magnet is energized. Thus each pulse of the groupfrequency current supplied to the tube causes the magnet to operate andclose the oathode circuit for a short intervalthrough contacts 5 4| and43, and at the same time interrupts" the plate circuit so that the tubewill be in condition for operation by the next pulse.

A third form of switch AS is shown in Figure 11b. Here a rotary switch5| is driven by a suitable motor Me, and the speed of rotation isautomatically regulated in accordance with the group frequency currentby a small synchronous type motor 52 mounted on the same shaft.

In using any of the forms of the switch AS or 1| in using. chopper disk41, the exact instant of operation of the switch or disk is adjustableby the phase controlling device 45 which may comprise any well knownadjustable phase shifting arrangement,

It will be understood that the two screengrids located at thetransmitting and receiving stations are of the same eifective length orsize and that the two transmission channels extending between the twostations are of the same effective 35 length. In case these two channelsare not of the same length, suitable loading devices may be interposedto balance the channels.

The operation of my invention is asfollows, referring to Figure 11:Assume that the chopper 80 disk CD is being used and that the chopperswitch CS is either short-circuited or placed in a position to completethe cathode circuit. When an opening in the disk CD passes in front ofthe transmitting cell, rays of light forming image 0' 85 on cathodecause electrons to be liberated from the cathode in the areas covered'bythe image. These electrons are caused to travel in straight lines fromcathode towards the anode l4; some of the electrons passing throughgrids I2 and I3. Since grids I2 and |3 are charged positively withrespect to the cathode I, each linear section of the two grids lyingwithin the path of the electrons will absorb or receive a certain numberof the electrons and produce current pulses in the grid circuitsproportional to the light intensity affecting each individual section.Each current pulse from each elementary linear section of each grid willbe transmitted as a distinct current pulse independently of the othercurrent pulses produced in other linear portions of each grid.Therefore, where the image of the objectbeing transmitted covers anextended area and contains areas of high and low light value, the cur--rent produced in each grid circuit will be a com- 55 plex current formedof many individual current pulses produced in the different linearsections of the grid. Since one grid is arranged in the form of a screenwith its bars horizontal and the other arranged with its bars vertical,each grid will have produced in it current pulses caused by the electronstream proceeding from each individual area of the image 0', but thecurrent pulse produced in one grid by a given elementary area may have alonger or a shorter path to the terminal of its grid than the same pulseproduced by the same area in the other grid, depending upon the positionof. the elementary area in the image. This action will be betterunderstood by reference to Figure 12.

Figure 12 is a simplified diagram wherein the elements l2 and I3represent the cathode and the two grids of the light sensitive cellemployed at the transmitting station A, and the elements 3, 5 and 6represent the fluorescent screen and the 75 'two grids in the receivingtube employed in receiving station 13. Line wires 36 and 31, togetherwith the common return wire 38, form, respectively, transmissionchannels corresponding to channels I and 2 in Figure 11. Batteries "and40 represent the sources of current necessary to produce and transmitthe current pulses over the two channels. For the purpose ofillustration, I have shown the grids formed of 9 bars each, although itwill be understood that the actual grids contain a greater number ofbars spaced very close together. The grids at the-transmitting andreceiving stations must be so connected that current pulses produced inthe two grids by any given elementary area of the image beingtransmitted must travel over transmission paths of equal distance beforethey coincide in position in front of the fluorescent screen 3. This maybe illustrated by tracing the paths of travel for current pulses set upin the vertical and the horizontal grids I2 and i3 by the elementaryarea represented by the small square at the center of the grid atstation A, it being remembered that the two transmission channels are ofthe same length. Referring to Figure 12 it will be seen that the currentpulse set up in the vertical grid must travel 4 bars of the grid beforereaching terminals l2, and the current pulse set up in horizontal gridby the square area must travel a distance of 4 bars before reaching thegrid terminals B. The two current pulses will travel over the twochannels and arrive at grid terminals 5 and 6' at the receiving stationsimultaneously. Assuming that the pulses travel through the grids at thesame speed, it will be seen that each pulse must travel through 4 barsof grid before the two pulses coincide in position, and this position ofcoincidence is located in the center of the grid, corresponding inposition to the elementary square at the transmitting station.

Taking next two current pulses produced by light from an elementary arealocated in the position of the small circle at the transmitting station;the current pulse produced in the vertical grid must travel through onlybar before reaching terminal l2, while the current pulse produced in thehorizontal grid must travel through 5 bar lengths before reaching theterminal l3. The current pulse transmitted over line 31 will arrive atterminal 6' before the current pulse set up in the horizontal grid l3arrives at the terminal 5', and the first current pulse will be 4 barsahead of the second. Accordingly, the two current pulses set up by theround elementary area will coincide at a point where grid wires 5 and 6intersect each other, and this point must be such that the distance fromterminal 6' is greater than the distance from the terminal 5 by 4 barlengths. It will be seen that this point of intersection is located atthe point of the small circle at station B, which corresponds inposition to the small circle at the transmitting station. In the samemanner, if current pulses are produced by an elementary area at thepoint represented by the triangle on the grids at the transmittingstation, by following through paths of equal length from this point, itwill be found that these pulses will coincide at the point indicated bythe small triangle on the grids at the receiving station. It will thusbe seen that the two current pulses produced by each of the threeelementary areas will coincide at the receiving station in positionscorresponding to the positions of the elementary areas at thetransmitting station. Since the current pulses transmitted vary inmagnitude in accordance with the light value of the elementary areaproducing the current pulse, the charges produced on the grids at thereceiving station at the point 5 of intersection will correspond inmagnitude to the light intensity of the elementary area beingtransmitted. These coinciding charges act cumulatively to cause anelectron streamto flow through the grids at this point and impinge upon10 the fluorescent screen 3 to produce a luminous spot whose intensitycorrespondstothelightvalue of the elementary area under consideration,it being understood that the cathode circuit is effective at the timethe charges are in proper 15 position. Since each elementary section ofeach grid produces an independent current pulse, the intensity of whichvaries in accordance with the light value of the elementary areaopposite each section, the resultant current transmitted over 20 the twochannels will comprise a series of pulses following each other in thesame linear arrangement as they are produced on the grid. These seriesof individual current pulses are transmitted to the receiving stationand impressed upon cor- 2| responding grids, and when the series in thetwo grids coincide, the original image will be reproduced on thefluorescent screen 3. A series of current pulses as described above willbe sent out over each channel each time the chopper disk CD uncovers thelens tube. Each series of pulses, produces a complete image at thereceiving station, and since the chopper disk rotates at a speed toproduce 16 or more-interruptions per second, the rapid succession ofslightly diiferent images at the receiving station appear as one movingimage. In order to render the reproduced image more discernible tothe'eye it is desirable to expose the screen 3 to vision only at theinstants at which the charges on the two grids are 40 in properposition, assuming that the switch AS is not being used and the cathodecircuit is active at all times. This is accomplished by the operation ofthe chopper disk 41, the rotational speed of which is regulated by theincoming picture 5 currents. The exact instant of exposure through, thedisk is adjusted by suitable adjustment of the phase shifter 45. Thespeed of the disk is such that the screen is exposed to view through anaperture in the disk each time a series of pulses 50 are in properposition on the two grids.

Instead of providing a constantly active cathode circuit and anintermittent viewing of screen 3, the chopper disk 41 may be omitted andthe automatic switch AS may be brought into 56 operation by placing theswitch 46 in the righthand position. The switch AS now-functions toperiodically close the cathode circuit only at the instants at which thecharges are in proper position. The instant of closing of the circuitmay be adjusted by adjustment of phase shifter 45. Any of the threedifferent forms of switch AS illustrated may be used. It will beunderstood that the stationary contact 43 may, if necessary, be mountedon the front side of movable contact 65 4| shown in Figures 11 and 11a.

While I have described a form of my invention in which two grids areemployed in the light sensitive cell at the transmitting station, andtwo transmission channels are provided to transmit 7 the impulses fromthe two grids to separate grids in a receiving tube at a distantstation, it is obvious that the system will operate with only one gridat each station and one transmission channel. However, by employing twogrids at 75 r 2,020,725 station, one arranged with its bars at rightangles'to the bars oi. the other grid, a better reproduction is obtainedand less distortion will result from the eiiects of static or liketransmission disturbances.

From the foregoing description of my invention it will be seen that dueto the new method circuit to produce balanced transmission circuits.

It will be understood that two separate carrier waves are not necessaryin the operation of my invention, but a single carrier wave may beemployed for the transmission of thecurrents derived from the two gridsof the transmitting tube by-employing any well known multiplextransmission system 'using a single carrier wave, and effectingmodulation of two channels 01' the carrier wave system by the twocurrents'derived from the two transmitting grids. Multiplex transmissionsystems suitable for this purpose, wherein a single carrier wave servesto transmit simultaneously a plurality of separate transmissions overseparate channels, are well known to those skilled in the art.

It will be obvious to one skilled in the art that the structural detailsof the elements employed in my television system may be modified invarious ways without departing from the spirit of the invention.

What I claim is:

a 1. In a television system the combination of a transmitting stationand, a receiving station,

a pair of transmission channels connecting said stations, each of saidchannels including a linear conductor arranged at each of said stations,

means at said transmitting station for forming an image of an object tobe transmitted, means for simultaneously impressing upon differentlinear portions of one of said transmission conductors current impulsescorresponding in intensity to the light values of successive elementaryareas of the image arranged in parallel lines crossing the image in onedirection, means for simultaneously impressing upon different linearsections of the second transmitting conductor current impulsescorresponding in intensity to the light values of successive elementaryareas of the image arranged in parallel lines crossing the image atright angles to said first parallel lines, means for periodicallyinterrupting the light rays forming said image, means at the receivingstation including one of said receiving conductors for distributing thecurrent impulses from one of said channels over an area in the sameorder in which said impulses were derived from said image, meansincluding said second receiving conductor for distributing the currentimpulses from the second channel over a like superimposed area in thesame order in which said impulses were derived from" said image, andmeans controlled by the joint action of said two receiving conductorsfor translating said superimposed. current impulses into correspondinglight variations.

2. In a television system the combination of a light sensitive cathodehaving an extended area, means for forming an image of an object to betransmitted on said area, an anode adjacent said cathode and comprisinga transmission conductor 6 arranged in the form of a grid having an areasubstantially as large as said cathode area, a second anode comprising asecond grid element having its bars arranged at right angles to the barsof said first grid element. a source oi. current 10 maintaining eachgrid element positive with re-' spect to said cathode, a transmissionchannel connected to each grid element and extending to a distantreceiving station, an electron emitting cathode at said receivingstation having an ex- 1 tended area, a grid element arranged in front ofsaid cathode comprising a transmission conductor formed as a grid, asecond grid element adjacent said first grid element and comprising asecond transmission conductor grid with its 2 bars arranged at rightangles to the bars of the 'flrst grid, 9. fluorescent plate anodelocated in line with said grids and said cathode, a source of currentfor maintaining said anode positive with respect to said cathode, saidgrids being connected to said transmission channels, and means forperiodically interrupting the light rays forming said image at saidtransmission station.

3. The method of transmatting optical images to a distance whichconsists in simultaneously impressing upon successive linear sections ofa transmission conductor, current impulses corresponding in intensity tothe light values of the successive elementary areas of the imagearranged in parallel lines crossing the-image in one direction,simultaneously impressing upon a second transmission conductor currentimpulses corresponding in intensity to the light values of successiveelementary areas of the image arranged in parallel lines crossing theimage at at right angles to the lines of said first receiving conductorforming an area superimposed on said first conductor area, andtranslating the conjoint action of said'impulses in said areas intocorresponding light variations.

4. The method of transmitting optical images to a distance whichconsists in simultaneously' impressing upon successive linear sectionsof a transmission conductor, current impulses corresponding in intensityto the light values of the successive elementary areas of the imagearranged in parallel lines crossing the image in one direction,simultaneously impressing upon a second transmission conductor currentimpulse corresponding in intensity to the light values of successiveelementary areas of the image arranged in parallel lines crossing theimage at right angles to said first parallel lines, transmitting saidtwo sets of current impulses to a distant receiving station overtransmission paths of equal length, distributing one set of impulsesover an area in the same order as they were derived at F thetransmitting station, distributing the other set of impulses over asecond area superimposed over the first area in a like manner, andtranslating the conjoint action of said impulses in said areas intocorresponding light variations.

5. A transmitting cell for a television system comprising an evacuatedenvelope containing a light sensitive cathode element having an extendedarea for receiving an image of the object to be transmitted, an anodearranged adjacent said cathode and comprising a continuous conductoriormed into a grid or substantially the same area as said cathode, asecond anode associated with said cathode and comprising a secondcontinuous conductor formed as a grid with its bars arranged at rightangles to the bars of the first grid, the bars in each of said gridsbeing connected in serial circuit relation but otherwise insulated fromeach other, said two grids being insulated from each other, and terminalconnections for each of said elements sealed into said envelope.

cathode and comprising a continuous conductor formed into a grid ofsubstantially the same area as said cathode, a second anode arranged infront of said first anode and comprising a second continuous conductorformed as a grid with its bars arranged at right angles to the bars ofthe first grid, the bars in each of said grids being connected in serialcircuit relation but otherwise insulated from each other, said two gridsbeing insulated from each other, and terminal connections for each ofsaid elements sealed into said envelope.

'7. A transmitting cell for a television system comprising an evacuatedenvelope containing a light sensitive cathode element having an extendedarea for receiving an image oi. the object to be transmitted, an anodearranged adjacent said cathode and comprising a continuous conductorformed into a grid 01' substantially the same area as said cathode, asecond anode arranged in 'front of said first anode and comprising asecond continuous conductor formed as a grid with its bars arranged atright angles to the bars of the first grid, the bars in each of saidgrids being connected in serial circuit relation but otherwise insulatedfrom each other, said two grids being insulated from each other, a plateanode element arranged parallel to said grids and in line with said gridand cathode elements, and terminal connections for each of said elementssealed into said envelope.

8. A transmitting cell for a television system comprising an evacuatedenvelope containing a light sensitive cathode element having an extendedarea for receiving an image of the object to be transmitted, an anodearranged adjacent said cathode and comprising a continuous conductorformed into a grid of substantially the same area as said cathode, thebars in each of said grids being connected in serial circuit relationbut otherwise insulated from each other, a second anode arranged infront of said first anode and comprising a second continuous conductorformed as a grid with its bars arranged at right angles to the bars 01the first grid, the bars in each of said grids being connected in serialcircuit relation but otherwise insulated from each other, said two gridsbeing insulated from each other, a plate-anode element arranged parallelto said grids and in line with said grid and cathode elements, and asource of infra-red rays arranged to act upon said cathode element.

9. A receiving tube for a television system comprising a glass. envelopecontaining an electron emitting cathode having an extended active area,an anode associated with said cathode comprising a continuous conductorformed into a grid area, a second grid anode. arranged parallel to thefirst grid anode and having its bars at right an- 5 glcs to the bars ofthe first grid, a fluorescent plate anode arranged parallel to said gridanodes and in line with said cathode, and terminal connections to eachor said elements sealed into said envelope. 1

10. In a television system the combination of a transmitting station anda receiving station, a transmission channel connecting said stations,said channel including a linear conductor arranged at each of saidstations, means at said 15 transmitting station for forming an image ofan object to be transmitted, means for simultaneously impressing upondiflerent linear portions of said transmission conductor currentimpulses corresponding in intensity to the light values of 20 successiveelementary areas 01' the image arranged in parallel lines crossing theimage in one direction, means for periodically interrupting the lightrays forming said image, means at the receiving station including saidreceiving con- 25 ductor for distributing the current impulses from saidchannel over an area in the same order in which said impulses werederived from said image, means for translating said current impulsesinto corresponding light variations, and means for rendering said lightvariations visible only at the instant when said current impulses are inproper position within said area.

11. In a television system the combination of a light sensitive cathodehaving an extended area, means for forming an image of an object to betransmitted on said area, an anode adjacent said cathode and comprisinga transmission conductor arranged in the form of a grid having an areasubstantially as large as said cathode area, a source of current formaintaining said grid element positive with respect to said cathode, atransmission channel extending to a distant re-. ceiving station, anelectron emitting cathode at said receiving station having an extendedarea, a grid element arranged in front of said cathode comprising atransmission conductor formed as a grid, a fluorescent plate anodelocated in line with said grid and said cathode, a source of current formaintaining said anode positive with respect to said cathode, said gridbeing connected to said transmission channel, means at the transmittingstation for periodically rendering the light sensitive cathodeeffective, and means at the receiving station for periodically renderingthe electron emitting cathode effective.

12. The method of transmitting optical images to a distance whichconsists in simultaneously impressing upon successive linear sections ofa transmission conductor, current impulses corresponding in intensity tothe light values of the successive elementary areas of the imagearranged in parallel lines crossing the imagein one direction,transmitting said current impulses to a distant receiving station,repeating said first and 5 second operations at a rate of the order ofsixteen or more times per second, at the receiving station, impressingsaid received impulses upon a transmission conductor arranged inparallel lines to form an area, translating said impulses in said areainto corresponding light variations, and periodically rendering saidlight variations visible only at the instant when said current impulsesare in proper position within said area.

13. The method or transmitting optical images 16 tended area, a gridelement arranged in front of,

to a distance which consists in simultaneously impressing uponsuccessive linear sections of a transmission conductor, current.impulses corresponding in intensity to the light values of thesuccessive elementary areas of the image arranged in parallel linescrossing theimage in one direction, transmitting said current impulsesto a distant receiving station, repeating said first and secondoperations at a rate oi the order 0! sixteen or more times per second,at the receiving station distributingsaid impulses 'overan area in thesame order as they were derived at the transmitting station, translatingsaid impulses in said area into corresponding light variations, andperiodically rendering said light variations visible only at the instantwhen said current impulses are in proper position within said area.

14. In a television system, the combination of a transmitting stationincluding a light sensitive cell comprising a light sensitive cathodehaving an extended area, an anode adjacent said cathode and comprising atransmission conductor arranged in the form of a grid having an areasubstantially as large as said cathode area and having its grid barsspaced apart a distance of the order of the dimension of an elementaryarea of the image to be transmitted, and a plate anode element mountedon the opposite side oi said grid from said cathode, means for formingan image of an object to be transmitted on said cathode, a source ofcurrent for maintaining said plate anode positive with respect to saidcathode, means for periodically interrupting the cathode circuit, a

transmission channel extending between said grid anode and a distantreceiving station, a receiving cell at said receiving station comprisingan electron emitting cathode having an extended area, a grid elementarranged in front of said cathode comprising a transmission conductorformed as a grid and connected to said transmission channel, afluorescent plate anode located in line with'said grid and said cathode,a source of current for maintaining said fluorescent anode positive withrespect to said electron emitting cathode, and means for periodicallyinterrupting the circuit of said electron emitting cathode in timedrelation with the current im pulses transmitted over said transmissionchannel.

15. In a television system the combination of a light sensitive cathodehaving an extended area, means for forming an image of an object to betransmitted on said area, an a'nhde adjacent said cathode and comprisinga transmission conductor arranged in the form of a grid having an areasubstantially as large as said cathode area, a source of current formaintaining said grid element positive with respect to said cathode, atransmission channel extending to a distant receiving station, means forperiodically opening and closing the circuit of the light sensitivecathode for transmitting periodic current impulses over said channel, anelectron emitting cathode at said receiving station having an exsaidcathode comprising a transmission conductor formed as a grid, afluorescent plate anode located in line with said grid and said cathode,a source of current for maintaining said anode positive 5 with respectto said cathode, said grid being connected to said transmission channel,and means at the receiving station responsive to the received periodicimpulses ior periodically opening and closing the circuit between thecathode and the 10 fluorescent plate.

16. A transmitting cell for a television system comprising an evacuatedenvelope containing a light sensitive cathode element having an extendedarea for receiving an image of the object 15 to be transmitted, an anodearranged adjacent said cathode and comprising a grid electrode oisubstantially the same area as said cathode and having its grid barsmutuallyinsulated from each other and spaced apart a distance of theorder of 20 the dimension of an elementary area of the image to betransmitted, means effectively connecting said grid bars in serialcircuit relation and terminal connections for each of said elementssealed into said envelope.

1'7. A transmitting cell for a television system comprising an evacuatedenvelope containing a light sensitive cathode element having an extendedarea for receiving an image of the object to be transmitted, an anodearranged adjacent said cathode and comprising a continuous conductorformed into a grid of substantially the same area as said cathode andhaving its grid bars connected in serial relation but otherwiseelectrically insulated from each other and spaced :1, apart a distanceof the order of the dimension of an elementary area of the image to betrans mitted, and terminal connections for each of, said elements sealedinto said envelope.

18. A receiving tube for a television system comprising a glass envelopecontaining an electron emitting cathode having an extended active area,a fluorescent plate anode arranged parallel to said cathode within saidenvelope, and a control electrode arranged between said cathode andanode comprising a continuous conductor formed into a grid having itsbars spaced apart a dis tance of the order of the dimension oi anelementary area of the picture to be reproduced and connected in serialcircuit relation but otherwise electrically insulated from each other.

19. A receiving tube for a television system comprising a glass envelopecontaining an electron emitting cathode having an extended active area,a fluorescent plate anode arranged parallel 55 to said cathode withinsaid envelope, 9. control electrode arranged between said cathode andanode and comprising a grid structure having its bars mutually insulatedfrom each other and spaced apart a distance of the order of thedimension or an elementary area or the picture to be reproduced, andmeans effectively connecting said grid bars in series circuit relation.

DONALD JEROME BAKER.

CERTIFICATE OF CORRECTION.

Patent No. 2,026,725. January 7, 1936.

DONALD JEROME BAKER.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 8,first column, lines 60, 61 and 62., claim 8, strike out the words "thebars in each of said grids being connected in serial circuit relationbut otherwise insulated from each other" and insert the same before "a"in second column, line 6, claim 9; and that the said Letters Patentshould be read with this correction there in that the same may conformto the record of the case in the Patent Office.

Signed and sealed this 18th day of February, A. D. 1936.

Leslie Frazer (Seal) Acting Commissioner of Patents.

